Disk drives are known in the art that use various kinds of disks, such as: optical disks, magneto-optical disks, flexible magnetic-recording disks, and similar disk data-storage devices. In particular, hard-disk drives (HDDs) have been widely used as indispensable data-storage devices for current computer systems. Moreover, HDDs have found widespread application to motion picture recording and reproducing apparatuses, car navigation systems, cellular phones, and similar devices, in addition to the computers, because of their outstanding information-storage characteristics.
A HDD includes a magnetic-recording disk and a head-slider; data on the magnetic-recording disk are read and written with the head-slider. To increase recording information-storage capacity per unit area on the magnetic-recording disk, areal density of recorded information is increased. However, reduction in recording bit length raises an issue that the areal density cannot be increased beyond a limiting value, known by the term of art, “superparamagnetic limit,” determined by thermal fluctuation in magnetization of the recording medium. Generally, the effects of the thermal fluctuation increase as the value of Ku·V/kT is smaller, where: Ku is a magnetic anisotropy constant of the recording medium; V is a minimum unit volume for magnetization in the recording medium; k is a Boltzmann constant; and, T is absolute temperature. Accordingly, Ku or V is increased so as to reduce the effect of the thermal fluctuation in the recording medium of the magnetic-recording disk.
In order to address this issue, as is known in the art, a perpendicular-magnetic-recording (PMR) method has been developed that writes with a magnetic signal perpendicularly on a bilayer PMR medium including a soft-magnetic underlayer with a probe-pole write head. This method can apply a stronger magnetic-recording field to the magnetic-recording disk. Therefore, a recording layer of a magnetic-recording disk with a large magnetic anisotropy constant, Ku, can be used. Moreover, in a magnetic-recording disk in the PMR method, an increase in V may be provided by growing magnetic particles in the film thickness direction while maintaining the magnetic particle diameter on the medium surface small, or maintaining the bit length small.
Another parameter affecting the areal density of recorded information on the PMR medium is the spacing between the thin-film magnetic-recording head and the recording surface of the magnetic-recording disk, known in the art as, “fly height,” of the thin-film magnetic-recording head in proximity with a recording surface of the magnetic-recording disk. The fly height may be controlled by a technique known in the art as, “thermal-fly-height control,” or “TFC”.
Engineers and scientists engaged in HDD manufacturing and development are interested in the design of thin-film magnetic-recording heads in HDDs that increase areal density to meet the rising demands of the marketplace for increased data-storage capacity, performance, and reliability.